From the foot wear news article:
Plantar fasciitis, according to the Mayo Clinic, is one of the most common causes of foot pain. It involves inflammation of a thick band of tissue that runs across the bottom of the foot and connects the heel bone to the toes (plantar Fascia).
It commonly causes stabbing pain that occurs with the first steps of the morning, and it eases as the day progresses and you move about. However, it can return after long periods of standing or rising after sitting.
Read more at the link: